She said that is called a "dead man's switch," because when a suicide attacker loses the grip on the switch, it sets off the detonation.

"So if they were shot and brought down, the bomb would still explode," Herridge explained.

She added that a big piece of the puzzle is if the suicide devices used in Brussels bear the same "signature" as those used the Paris attacks in November, since it would suggest a larger network of ISIS followers and operatives in Western Europe.

Herridge said the focus of the investigation will now be on identifying the suspects through DNA, which will enable authorities to trace their network of contacts.

Watch more above.

UPDATE 2:00pm ET: The man seen on the right in the photo is being hunted by authorities.

Greg Palkot reported the latest moments ago, saying police believe the two other men - dressed in black - were suicide bombers.

An un-detonated explosive vest was also found at the airport. Herridge further reported that the man in white appears to be in disguise, possibly with a fake nose.

She said that it's common in suicide bombings for the attackers to have an "escort" to make sure they reach the destination.

ISIS has taken responsibility since the attack. Herridge said ISIS has not been known to take responsibility for attacks they did not commit.

Herridge said it appears that the attack had been in the works for a while and was expedited following the capture of a Paris terror attack suspect in Brussels.

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